Natural gas liquid fractionation plant cooling capacity and potable water generation using integrated vapor compression-ejector cycle and modified multi-effect distillation system

ABSTRACT

Certain aspects of natural gas liquid fractionation plant cooling capacity and potable water generation using integrated vapor compression-ejector cycle and modified multi-effect distillation system can be implemented as a system. The system includes a waste heat recovery heat exchanger network thermally coupled to multiple heat sources of a Natural Gas Liquid (NGL) fractionation plant. The heat exchanger network is configured to recover at least a portion of heat generated at the multiple heat sources. The system includes a first sub-system thermally coupled to the waste heat recovery heat exchanger to receive at least a first portion of heat recovered by the heat exchanger network. The first sub-system is configured to perform one or more operations using at least the first portion of heat recovered by the heat exchanger network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims the benefit of priority to U.S. Application Ser.No. 62/542,687 entitled “Utilizing Waste Heat Recovered From Natural GasLiquid Fractionation Plants”, which was filed on Aug. 8, 2017, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to operating industrial facilities, for example,a natural gas liquid fractionation plant or other industrial facilitiesthat include operating plants that generate heat, for example, a naturalgas liquid fractionation plant.

BACKGROUND

Natural gas liquid (NGL) processes are chemical engineering processesand other facilities used in petroleum refineries to transform naturalgas into products, for example, liquefied petroleum gas (LPG), gasoline,kerosene, jet fuel, diesel oils, fuel oils, and such products. NGLfacilities are large industrial complexes that involve many differentprocessing units and auxiliary facilities, for example, utility units,storage tanks, and such auxiliary facilities. Each refinery can have itsown unique arrangement and combination of refining processes determined,for example, by the refinery location, desired products, economicconsiderations, or such factors. The NGL processes that are implementedto transform the natural gas into the products such as those listedearlier can generate heat, which may not be reused, and byproducts, forexample, greenhouse gases (GHG), which may pollute the atmosphere. It isbelieved that the world's environment has been negatively affected byglobal warming caused, in part, due to the release of GHG into theatmosphere.

SUMMARY

This specification describes technologies relating to cooling capacitygeneration, power generation or potable water production from waste heatin a natural gas liquid (NGL) fractionation plant.

The present disclosure includes one or more of the following units ofmeasure with their corresponding abbreviations, as shown in Table 1:

TABLE 1 Unit of Measure Abbreviation Degrees Celsius ° C. Megawatts MWOne million MM British thermal unit Btu Hour h Pounds per square inch(pressure) psi Kilogram (mass) Kg Second S Cubic meters per day m³/dayFahrenheit F.

Certain aspects of the subject matter described here can be implementedas a system. In an example implementation, the system includes a wasteheat recovery heat exchanger network thermally coupled to multiple heatsources of a Natural Gas Liquid (NGL) fractionation plant. The heatexchanger network is configured to recover at least a portion of heatgenerated at the multiple heat sources. The system includes a firstsub-system thermally coupled to the waste heat recovery heat exchangerto receive at least a first portion of heat recovered by the heatexchanger network. The first sub-system is configured to perform one ormore operations using at least the first portion of heat recovered bythe heat exchanger network.

In an aspect combinable with the example implementation, the systemincludes a second sub-system thermally coupled to the waste heatrecovery heat exchanger to receive at least a second portion of heatrecovered by the heat exchanger network. The second sub-system isseparate and distinct from the first sub-system, and is configured toperform one or more operations using at least the second portion of heatrecovered by the heat exchanger network.

In another aspect combinable with any of the previous aspects, thesystem includes a control system connected to the heat exchanger networkand the first sub-system, or the heat exchanger network and the secondsub-system, or the heat exchanger network, the first sub-system and thesecond sub-system. The control system is configured to flow fluidsbetween the NGL fractionation plant, the heat exchanger network one orboth of the first sub-system or the second sub-system.

In another aspect combinable with any of the previous aspects, thefluids include one or more of a NGL fractionation plant stream or abuffer fluid.

In another aspect combinable with any of the previous aspects, themultiple heat sources include first multiple sub-units of the NGLfractionation plant including a propane dehydration section, ade-propanizer section, a butane de-hydrator section, and a de-butanizersection, a second multiple sub-units of the NGL fractionation plantincluding a de-pentanizer section, an Amine-Di-Iso-Propanol (ADIP)regeneration section, a natural gas de-colorizing section, a propanevapor recovery section and a propane product refrigeration section, andthird multiple sub-units of the NGL fractionation a propane productsub-cooling section, a butane product refrigeration section, an ethaneproduction section and a Reid Vapor Pressure (RVP) control section.

In another aspect combinable with any of the previous aspects, the heatexchanger network includes multiple heat exchangers.

In another aspect combinable with any of the previous aspects, themultiple heat exchangers include a first subset comprising one or moreof the multiple heat exchangers thermally coupled to the first pluralityof sub-units of the NGL fractionation plant.

In another aspect combinable with any of the previous aspects, the firstsubset includes a first heat exchanger thermally coupled to the propanedehydration section, and configured to heat a first buffer stream usingheat carried by a propane de-hydration outlet stream from the propanede-hydration section. The first subset includes a second heat exchangerthermally coupled to the de-propanizer section, and configured to heat asecond buffer stream using heat carried by a de-propanizer overheadoutlet stream from the de-propanizer section. The first subset includesa third heat exchanger thermally coupled to the butane de-hydratorsection, and configured to heat a third buffer stream using heat carriedby a butane de-hydrator outlet stream. The first subset includes afourth heat exchanger thermally coupled to the de-butanizer section, andconfigured to heat a fourth buffer stream using heat carried by ade-butanizer overhead outlet stream from the de-butanizer section. Thefirst subset includes a fifth heat exchanger thermally coupled to thede-butanizer section, and configured to heat a fifth buffer stream usingheat carried by a de-butanizer bottoms outlet stream from thede-butanizer section.

In another aspect combinable with any of the previous aspects, themultiple heat exchangers include a second subset including one or moreof the multiple heat exchangers thermally coupled to the secondplurality of sub-units of the NGL fractionation plant.

In another aspect combinable with any of the previous aspects, thesecond subset includes a sixth heat exchanger thermally coupled to thede-pentanizer section, and configured to heat a sixth buffer streamusing heat carried by a de-pentanizer overhead outlet stream from thede-pentanizer section. The second subset includes a seventh heatexchanger thermally coupled to the ADIP regeneration section, andconfigured to heat a seventh buffer stream using heat carried by an ADIPregeneration section overhead outlet stream. The second subset includesan eighth heat exchanger thermally coupled to the ADIP regenerationsection, and configured to heat an eighth buffer stream using heatcarried by an ADIP regeneration section bottoms outlet stream. Thesecond subset includes a ninth heat exchanger thermally coupled to thenatural gas de-colorizing section, and configured to heat a ninth bufferstream using heat carried by a natural gas de-colorizing sectionpre-flash drum overhead outlet stream. The second subset includes atenth heat exchanger thermally coupled to the natural gas de-colorizingsection, and configured to heat a tenth buffer stream using heat carriedby a natural gas de-colorizer overhead outlet stream. The second subsetincludes an eleventh heat exchanger thermally coupled to the propanevapor recovery section, and configured to heat an eleventh buffer streamusing heat carried by a propane vapor recovery compressor outlet stream.The third subset includes a twelfth heat exchanger thermally coupled tothe propane product refrigeration section, and configured to heat atwelfth buffer stream using heat carried by a propane refrigerationcompressor outlet stream from the propane product refrigeration section.

In another aspect combinable with any of the previous aspects, themultiple heat exchangers include a third subset including one or more ofthe multiple heat exchangers thermally coupled to the third plurality ofsub-units of the NGL fractionation plant.

In another aspect combinable with any of the previous aspects, the thirdsubset includes a thirteenth heat exchanger thermally coupled to thepropane product sub-cooling, and configured to heat a thirteenth bufferstream using heat carried by a propane main compressor outlet streamfrom the propane product sub-cooling section. The third subset includesa fourteenth heat exchanger thermally coupled to the butane productrefrigeration section, and configured to heat a fourteenth buffer streamusing heat carried by a butane refrigeration compressor outlet streamfrom the butane product refrigeration section. The third subset includesa fifteenth heat exchanger thermally coupled to the ethane productionsection, and configured to heat a fifteenth buffer stream using heatcarried by an ethane dryer outlet stream. The third subset includes asixteenth heat exchanger thermally coupled to the RVP control section,and configured to heat a sixteenth buffer stream using heat carried by aRVP control column overhead outlet stream.

In another aspect combinable with any of the previous aspects, thesystem includes a storage tank configured to store the buffer streams.The control system is configured to flow the buffer streams from thestorage tank to the heat exchanger network.

In another aspect combinable with any of the previous aspects, thebuffer stream includes pressurized water.

In another aspect combinable with any of the previous aspects, the firstsub-system includes a modified multi-effect-distillation (MED) systemconfigured to produce potable water using at least the portion of heatrecovered by the heat exchanger network. The MED system includesmultiple trains. Each train is configured to receive the heated bufferfluid from the heat exchanger network and to produce potable water usingthe heat carried by the heated buffer fluid.

In another aspect combinable with any of the previous aspects, the MEDsystem includes three trains. A first train includes six effects, asecond train includes four effects and a third train includes twoeffects.

In another aspect combinable with any of the previous aspects, thesecond sub-system includes a cooling sub-system configured to generatecooling capacity to cool at least a portion of the NGL fractionationplant.

In another aspect combinable with any of the previous aspects, thecooling sub-system includes a mono-refrigerant dual vaporcompressor-ejector cycle.

In another aspect combinable with any of the previous aspects, thecompressor-ejector cycle includes a first propane stream that isvaporized to generate the cooling capacity.

In another aspect combinable with any of the previous aspects, the thirdsubset includes a third subset of heat exchangers including aseventeenth heat exchanger thermally coupled to the de-ethanizersection, and configured to heat the first propane stream using heatcarried by a de-ethanizer refrigeration compressor outlet stream fromthe de-ethanizer section.

In another aspect combinable with any of the previous aspects, the MEDsystem can include a first phase comprising three trains. A first trainin the first phase can include six effects, a second train in the firstphase can include four effects and a third train in the first phase caninclude two effects.

In another aspect combinable with any of the previous aspects, the MEDsystem can include a second phase including three trains. The secondphase can be connected in parallel with the first phase. A fourth trainin the second phase can include five effects, a fifth train in thesecond phase can include four effects and a sixth train in the secondphase can include two effects.

In another aspect combinable with any of the previous aspects, the MEDsystem can include a third phase including one train, the third phaseconnected in parallel with the second phase.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the detailed description. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of an example of a low grade waste heatrecovery system.

FIG. 1B is a schematic diagram of a propane de-hydration section wasteheat recovery system in a NGL fractionation plant.

FIG. 1C is a schematic diagram of a de-propanizer section waste heatrecovery system in a NGL fractionation plant.

FIG. 1D is a schematic diagram of a butane de-hydrator section wasteheat recovery system in a NGL fractionation plant.

FIG. 1E is a schematic diagram of a de-butanizer section waste heatrecovery system in a NGL fractionation plant.

FIG. 1F is a schematic diagram of a de-pentanizer section waste heatrecovery system in a NGL fractionation plant.

FIG. 1G is a schematic diagram of an ADIP regeneration section wasteheat recovery system in a NGL fractionation plant.

FIG. 1H is a schematic diagram of a natural gasoline de-colorizingsection waste heat recovery system in a NGL fractionation plant.

FIG. 1I is a schematic diagram of a propane tank vapor recovery sectionwaste heat recovery system in a NGL fractionation plant.

FIG. 1J is a schematic diagram of a propane product refrigerationsection waste heat recovery system in a NGL fractionation plant.

FIG. 1K is a schematic diagram of a propane product sub-cooling sectionwaste heat recovery system in a NGL fractionation plant.

FIG. 1L is a schematic diagram of a butane product refrigeration wasteheat recovery system in a NGL fractionation plant.

FIG. 1M is a schematic diagram of an ethane production section wasteheat recovery system in a NGL fractionation plant.

FIG. 1N is a schematic diagram of a natural gasoline vapor pressurecontrol section waste heat recovery system in a NGL fractionation plant.

FIG. 1O is a schematic diagram of an integrated, customized,mono-refrigerant dual vapor compressor-ejector cycle.

FIG. 1P is a schematic diagram representing an example of a modified MEDsystem configured to produce potable water using pressurized waterheated by a heat exchanger network.

DETAILED DESCRIPTION

NGL Plant

Gas processing plants can purify raw natural gas or crude oil productionassociated gases (or both) by removing common contaminants such aswater, carbon dioxide and hydrogen sulfide. Some of the substances whichcontaminate natural gas have economic value and can be processed or soldor both. Upon the separation of methane gas, which is useful as salesgas for houses and power generation, the remaining hydrocarbon mixturein liquid phase is called natural gas liquids (NGL). The NGL isfractionated in a separate plant or sometimes in the same gas processingplant into ethane, propane and heavier hydrocarbons for severalversatile uses in chemical and petrochemical as well as transportationindustries. The NGL fractionation plant uses the following processes orsections: fractionation, product treating, and natural gasolineprocessing. The fractionation processes or sections can include heatsources (also commonly referred to as streams) including, but notlimited to, a propane condenser, a propane refrigerant condenser, anaphtha cooler, a de-pentanizer condenser, an amine-di-iso-propanol(ADIP) cooler, a regenerator overhead (OVHD) condenser, a Reid vaporpressure (RVP) column condenser, a de-propanizer condenser, ade-butanizer condenser, or combinations thereof. The product treatingprocesses or sections can include the following non-limiting heatsources: a propane dehydrator condenser, a butane dehydrator condenser,a propane condenser, an air-cooled condenser, a regeneration gas cooler,and a butane condenser, or combinations thereof. The natural gasolineprocessing processes or sections can include, but are not limited to, anatural gasoline (NG) flash vapor condenser, a NG de-colorizercondenser, or combinations thereof.

Fractionation Section

Fractionation is the process of separating the different components ofnatural gas. Separation is possible because each component has adifferent boiling point. At temperatures less than than the boilingpoint of a particular component, that component condenses to a liquid.It is also possible to increase the boiling point of a component byincreasing the pressure. By using columns operating at differentpressures and temperatures, the NGL fractionation plant is capable ofseparating ethane, propane, butane, pentane, or combinations thereof(with or without heavier associated hydrocarbons) from NGL fractionationfeeds. De-ethanizing separates ethane from C2+ NGL, where C2 refers to amolecule containing two carbon atoms (ethane), and where C2+ refers to amixture containing molecules having two or more carbon atoms, forexample, a NGL containing C2, C3, C4, C5 can be abbreviated as “C2+NGL”. De-propanizing and de-butanizing separate propane and butane,respectively, from C3+ NGL and C4+ NGL, respectively. Because theboiling points of heavier natural gases are closer to each other, suchgases can be harder to separate compared to lighter natural gases. Also,a rate of separation of heavier components is less than that ofcomparatively lighter components. In some instances, the NGLfractionation plant can implement, for example, about 45 distillationtrays in the de-ethanizer, about 50 trays in the de-propanizer, andabout 55 trays in the de-butanizer.

The fractionation section can receive a feed gas containing C2+ NGL fromgas plants, which are upstream plants that condition and sweeten thefeed gas, and produce a sales gas, such as a C1/C2 mixture, where C1 isabout 90%, as a final product. The C2+ NGL from gas plants can befurther processed in the NGL fractionation plant for C2+ recovery. Fromfeed metering or surge unit metering (or both), feed flows to the threefractionation modules, namely, the de-ethanizing module, thede-propanizing module and the de-butanizing module, each of which isdescribed later.

De-Ethanizer Module (or De-Ethanizer Column)

The C2+ NGL is pre-heated before entering the de-ethanizer column forfractionation. The separated ethane leaves the column as overhead gas.The ethane gas is condensed by a closed-loop propane refrigerationsystem. After being cooled and condensed, the ethane is a mixture of gasand liquid. The liquid ethane is separated and pumped back to the top ofthe column as reflux. The ethane gas is warmed in an economizer and thensent to users. The bottoms product from the de-ethanizer reboiler is C3+NGL, which is sent to the de-propanizer module.

De-Propanizer Module (or De-Propanizer Column)

From the de-ethanizer module, C3+ NGL enters the de-propanizer modulefor fractionation. The separated propane leaves the column as overheadgas. The gas is condensed using coolers. The propane condensate iscollected in a reflux drum. Some of the liquid propane is pumped back tothe column as reflux. The rest of the propane is either treated or sentto users as untreated product. The bottoms product from the depropanizerreboiler, C4+ is then sent to the de-butanizer module

De-Butanizer Module (or De-Butanizer Column)

C4+ enters the de-butanizer module for fractionation. The separatedbutane leaves the column as overhead gas. The gas is condensed usingcoolers. The butane condensate is collected in a reflux drum. Some ofthe liquid butane is pumped back to the column as reflux. The rest ofthe butane is either treated or sent to users as untreated product. Thebottoms product from the debutanizer reboiler, C5+ natural gas (NG) goeson to a RVP control section (which may also be referred to as a rerununit), which will be discussed in greater detail in a later section.

Product Treating Section

While ethane requires no further treatment, propane and butane productsare normally treated to remove hydrogen sulfide (H₂S), carbonyl sulfide(COS), and mercaptan sulfur (RSH). Then, the products are dried toremove any water. All exported product is treated, while untreatedproducts can go to other industries. As described later, propanereceives ADIP treating, MEROX™ (Honeywell UOP; Des Plaines, Ill.)treating, and dehydration. Butane receives MEROX treating, anddehydration.

ADIP Treating Section

ADIP is a solution of di-isopropanol amine and water. ADIP treatingextracts H₂S and COS from propane. The ADIP solution, through contactwith the sour propane, absorbs the H₂S and COS. The ADIP solution firstcontacts the sour propane in an extractor. In the extractor, the ADIPabsorbs most of the H₂S and some of the COS. The propane then passesthrough a mixer/settler train where the propane contacts with ADIPsolution to extract more H₂S and COS. This partially sweetened propaneis cooled and then washed with water to recover the ADIP entrained withthe propane. The propane is then sent to MEROX treating, which isdescribed later. The rich ADIP that has absorbed the H₂S and COS leavesthe bottom of the extractor and is regenerated into lean ADIP for reuse.The regenerator column has a temperature and pressure that are suitablefor acid gas removal. When the rich ADIP enters the regenerator, theentrained acid gases are stripped. As the acid gases leaves theregenerator as overhead, any free water is removed to prevent acidformation. The acid gases are then sent to flare. The lean ADIP leavesthe extractor bottom and is cooled and filtered. Lean ADIP returns tothe last mixer/settler and flows back through the system in thecounter-current direction of the propane to improve contact between thepropane and ADIP, which improves H₂S and COS extraction.

C3/C4 MEROX Treating Section

MEROX treating removes mercaptan sulfur from C3/C4 product. Mercaptansare removed using a solution of sodium hydroxide (NaOH), also known bythe commercial name caustic soda (hereinafter referred to as “caustic”)and MEROX. The MEROX catalyst facilitates the oxidation of mercaptans todisulfides. The oxidation takes place in an alkaline environment, whichis provided by using the caustic solution. MEROX treating for C3 and C4is similar. Both products are prewashed with caustic to remove anyremaining traces of H₂S, COS, and CO₂. This prevents damage to thecaustic that is used in MEROX treating. After prewashing, product flowsto an extractor, where a caustic solution with MEROX catalyst contactswith the product. The caustic/catalyst solution converts the mercaptansinto mercaptides. The sweetened product, which is lean on acid gases,leaves the extractor as overhead and any remaining caustic is separated.Caustic leaves the bottom of both product extractors rich withmercaptides. The rich caustic is regenerated into lean caustic forreuse. The C3/C4 extraction sections share a common caustic regenerationsection, namely, an oxidizer. Before entering the bottom of theoxidizer, the rich caustic is injected with MEROX catalyst to maintainproper catalyst concentration, heated, and mixed with process air. Inthe oxidizer, the mercaptides are oxidized into disulfides. The mixtureof disulfides, caustic, and air leave the oxidizer as overhead. The air,disulfide gases, and disulfide oil are separated from the regeneratedcaustic. The regenerated caustic is pumped to the C3/C4 extractor.Regenerated caustic with any residual disulfides is washed with NG inthe NG wash settler.

C3/C4 Dehydration Section

Propane or butane products (or both) contain water when they leave MEROXtreating. Dehydration removes moisture in such products throughadsorption before the products flow to refrigeration and storage. Thedehydration processes for C3 and C4 are similar. Both C3/C4 dehydrationsections have two de-hydrators containing molecular sieve desiccantbeds. One de-hydrator is in service while the other undergoesregeneration. Regeneration consists of heating the sieve beds to removemoisture, then cooling the beds before reuse. During drying, productflows up and through the molecular sieve bed, which adsorbs (that is,binds to its surface) moisture. From the top of the de-hydrator, dryC3/C4 products flow to refrigeration.

Natural Gasoline (NG) Processing Section

NG processing includes RVP control, de-colorizing and de-pentanizingsections.

RVP Control Section

A Reid vapor pressure (RVP) control section (or rerun unit) is afractionator column that receives the C5+NG from the debutanizer bottom.The RVP control section collects a pentane product. The RVP controlsection can be used to adjust the RVP of the pentane product at a rerunfractionator overhead before the pentane product is sent to a pentanestorage tank. RVP is a measure of the ability of a hydrocarbon tovaporize. RVP (sometimes called volatility) is an importantspecification in gasoline blending. The RVP control section stabilizesthe RVP of NG by removing small amounts of pentane. Depending onoperational requirements, the RVP control section can be totally orpartially bypassed. NG from the debutanizer bottoms goes to the RVPcolumn where a controlled amount of pentane is stripped and leaves thecolumn as overhead gas. As in NGL fractionation, the overhead gas iscondensed with coolers, and some of the condensate is pumped back to thecolumn as reflux. The remaining pentane is cooled and sent to storage.If the RVP column bottoms product (NG) meets color specifications, it issent to storage. If not, it is sent to decolorizing.

De-Colorizing Section

The de-colorizing section removes color bodies from NG. Color bodies aretraces of heavy ends found in the de-butanizer bottoms product. Otherimpurities such as corrosion products from the pipeline may also bepresent. These must be removed for NG to meet the color specification.De-colorizer feed can be RVP column bottoms product or de-butanizerbottoms product, or a combination of both. Additional natural gasolinecan also be supplied from other facilities to maintain a hexane plus(C6+) product supply. If de-colorizing is needed, NG first passesthrough a pre-flash-drum. A large portion of the lighter NG componentsvaporizes and leaves the drum as overhead. The heavier NG componentsremain along with the color bodies and are fed to the de-colorizercolumn, where the remaining color bodies are separated. The NG leavesthe de-colorizer as overhead gas and is condensed and collected in theNG product drum, with some pumped back to the column as reflux. Overheadfrom the column and flash drum are joined and pumped to either thede-pentanizer (described later) or cooled and sent to storage in thefeed product surge unit. The color bodies leave the de-colorizer asbottoms product and are pumped to the feed and surge unit to be injectedinto a crude line.

De-Pentanizing Section

De-pentanizing uses a fractionation column to produce a pentane overheadproduct and a C6+ bottoms product. Both the pentane product and the C6+bottoms product are separately fed to storage or downstream thepetrochemical plants. The feed to the de-pentanizer is the NG productstream from the de-colorizing section. Feed can be increased ordecreased based on the demand for C6+ bottoms product. If the NGLfractionation plant NG production cannot meet demand, NG can be importedfrom oil refineries. The de-colorized NG is preheated before enteringthe de-pentanizer. The separated pentane leaves the column as overheadgas. The overhead condensers cool the overhead stream, and some ispumped back to the column as reflux. The remaining pentane is cooled andsent to storage. Light NG in the bottoms is vaporized and returned toheat the de-pentanizer. The remaining bottoms product is cooled and sentto storage as C6+.

Table 2 lists duty per train of major waste heat streams in an exampleof an NGL fractionation plant.

TABLE 2 Duty/train Stream Name (MMBtu/h) Propane refrigerant condenser94 Propane de-hydration condenser 22 Butane de-hydrator condenser 9Naphtha cooler 11 De-pentanizer condenser 100 ADIP cooler 73 RegeneratorOVHD condenser 18 NG flash vapor condenser 107 NG de-colorizer condenser53 Natural gasoline (cooling) process 29 propane condenser Fractionationpropane condenser 81 Air cooled condenser 16 Regeneration gas cooler 22RVP column condenser 36 Butane condenser 49 De-propanizer condenser 194De-butanizer condenser 115

In Table 2, “Duty/train” represents each stream's thermal duty inmillions Btu per hour (MMBtu/h) per processing train. A typical NGLfractionation plant includes three to four processing trains.

The systems described in this disclosure can be integrated with a NGLfractionation plant to make the fractionation plant more energyefficient or less polluting or both. In particular, the energyconversion system can be implemented to recover low grade waste heatfrom the NGL fractionation plant. Low grade waste heat is characterizedby a temperature difference between a source and sink of the low gradeheat steam being between 65° C. and 232° C. (150° F. and 450° F.). TheNGL fractionation plant is an attractive option for integration withenergy conversion systems due to a large amount of low grade waste heatgenerated by the plant and an absence of a need for deep cooling. Deepcooling refers to a temperature that is less than ambient that uses arefrigeration cycle to maintain.

The low grade waste heat from an NGL fractionation plant can be used forcommodities such as carbon-free power generation, cooling capacitygeneration, potable water production from sea water, or combinationsthereof. Low grade waste heat is characterized by a temperature rangingbetween 65° C. and 232° C. (150° F. to 450° F.). The waste heat can beused for the mono-generation, co-generation, or tri-generation of one ormore or all of the commodities mentioned earlier. Low grade waste heatfrom the NGL fractionation plant can be used to provide in-plantsub-ambient cooling, thus reducing the consumption of power or fuel (orboth) of the plant. Low grade waste heat from the NGL fractionationplant can be used to provide ambient air conditioning or cooling in theindustrial community or in a nearby non-industrial community, thushelping the community to consume energy from alternative sources. Inaddition, the low grade waste heat can be used to desalinate water andproduce potable water to the plant and adjacent community. An NGLfractionation plant is selected for low grade waste heat recoverybecause of a quantity of low grade waste heat available from the NGLfractionation plant as well as a cooling requirement of the plant toambient temperature cooling (instead of deep cooling).

The energy conversion systems described in this disclosure can beintegrated into an existing NGL fractionation plant as a retrofit or canbe part of a newly constructed NGL fractionation plant. A retrofit to anexisting NGL fractionation plant allows the carbon-free powergeneration, and fuel savings advantages offered by the energy conversionsystems described here to be accessible with a reduced capitalinvestment. For example, the energy conversion systems described herecan produce one or more or all of substantially between 35 MW and 40 MW(for example, 37 MW) of carbon-free power, substantially between 100,000and 150,000 m³/day (for example, 120,000 m³/day) of desalinated water,and substantially between 350 MM BTU/h and 400 MM BTU/h (for example,388 MM BTU/h) of cooling capacity for in-plant or community utilizationor both.

As described later, the systems for waste heat recovery and re-use fromthe NGL fractionation plant can include modified multi-effectdistillation (MED) systems, customized Organic Rankine Cycle (ORC)systems, unique ammonia-water mixture Kalina cycle systems, customizedmodified Goswami cycle systems, mono-refrigerant specific vaporcompression-ejector-expander triple cycle systems, or combinations ofone or more of them. Details of each disclosure are described in thefollowing paragraphs.

Heat Exchangers

In the configurations described in this disclosure, heat exchangers areused to transfer heat from one medium (for example, a stream flowingthrough a plant in a NGL fractionation plant, a buffer fluid or suchmedium) to another medium (for example, a buffer fluid or differentstream flowing through a plant in the NGL fractionation plant). Heatexchangers are devices which transfer (exchange) heat typically from ahotter fluid stream to a relatively less hotter fluid stream. Heatexchangers can be used in heating and cooling applications, for example,in refrigerators, air conditions or such cooling applications. Heatexchangers can be distinguished from one another based on the directionin which fluids flow. For example, heat exchangers can be parallel-flow,cross-flow or counter-current. In parallel-flow heat exchangers, bothfluid involved move in the same direction, entering and exiting the heatexchanger side-by-side. In cross-flow heat exchangers, the fluid pathruns perpendicular to one another. In counter-current heat exchangers,the fluid paths flow in opposite directions, with one fluid exitingwhether the other fluid enters. Counter-current heat exchangers aresometimes more effective than the other types of heat exchangers.

In addition to classifying heat exchangers based on fluid direction,heat exchangers can also be classified based on their construction. Someheat exchangers are constructed of multiple tubes. Some heat exchangersinclude plates with room for fluid to flow in between. Some heatexchangers enable heat exchange from liquid to liquid, while some heatexchangers enable heat exchange using other media.

Heat exchangers in a NGL fractionation plant are often shell and tubetype heat exchangers which include multiple tubes through which fluidflows. The tubes are divided into two sets—the first set contains thefluid to be heated or cooled; the second set contains the fluidresponsible for triggering the heat exchange, in other words, the fluidthat either removes heat from the first set of tubes by absorbing andtransmitting the heat away or warms the first set by transmitting itsown heat to the fluid inside. When designing this type of exchanger,care must be taken in determining the correct tube wall thickness aswell as tube diameter, to allow optimum heat exchange. In terms of flow,shell and tube heat exchangers can assume any of three flow pathpatterns.

Heat exchangers in NGL facilities can also be plate and frame type heatexchangers. Plate heat exchangers include thin plates joined togetherwith a small amount of space in between, often maintained by a rubbergasket. The surface area is large, and the corners of each rectangularplate feature an opening through which fluid can flow between plates,extracting heat from the plates as it flows. The fluid channelsthemselves alternate hot and cold liquids, meaning that the heatexchangers can effectively cool as well as heat fluid. Because plateheat exchangers have large surface area, they can sometimes be moreeffective than shell and tube heat exchangers.

Other types of heat exchangers can include regenerative heat exchangersand adiabatic wheel heat exchangers. In a regenerative heat exchanger,the same fluid is passed along both sides of the exchanger, which can beeither a plate heat exchanger or a shell and tube heat exchanger.Because the fluid can get very hot, the exiting fluid is used to warmthe incoming fluid, maintaining a near constant temperature. Energy issaved in a regenerative heat exchanger because the process is cyclical,with almost all relative heat being transferred from the exiting fluidto the incoming fluid. To maintain a constant temperature, a smallquantity of extra energy is needed to raise and lower the overall fluidtemperature. In the adiabatic wheel heat exchanger, an intermediateliquid is used to store heat, which is then transferred to the oppositeside of the heat exchanger. An adiabatic wheel consists of a large wheelwith threads that rotate through the liquids—both hot and cold—toextract or transfer heat. The heat exchangers described in thisdisclosure can include any one of the heat exchangers described earlier,other heat exchangers, or combinations of them.

Each heat exchanger in each configuration can be associated with arespective thermal duty (or heat duty). The thermal duty of a heatexchanger can be defined as an amount of heat that can be transferred bythe heat exchanger from the hot stream to the cold stream. The amount ofheat can be calculated from the conditions and thermal properties ofboth the hot and cold streams. From the hot stream point of view, thethermal duty of the heat exchanger is the product of the hot stream flowrate, the hot stream specific heat, and a difference in temperaturebetween the hot stream inlet temperature to the heat exchanger and thehot stream outlet temperature from the heat exchanger. From the coldstream point of view, the thermal duty of the heat exchanger is theproduct of the cold stream flow rate, the cold stream specific heat anda difference in temperature between the cold stream outlet from the heatexchanger and the cold stream inlet temperature from the heat exchanger.In several applications, the two quantities can be considered equalassuming no heat loss to the environment for these units, particularly,where the units are well insulated. The thermal duty of a heat exchangercan be measured in watts (W), megawatts (MW), millions of BritishThermal Units per hour (Btu/hr), or millions of kilocalories per hour(Kcal/h). In the configurations described here, the thermal duties ofthe heat exchangers are provided as being “about X MW,” where “X”represents a numerical thermal duty value. The numerical thermal dutyvalue is not absolute. That is, the actual thermal duty of a heatexchanger can be approximately equal to X, greater than X or less thanX.

Flow Control System

In each of the configurations described later, process streams (alsocalled “streams”) are flowed within each plant in a NGL fractionationplant and between plants in the NGL fractionation plant. The processstreams can be flowed using one or more flow control systems implementedthroughout the NGL fractionation plant. A flow control system caninclude one or more flow pumps to pump the process streams, one or moreflow pipes through which the process streams are flowed and one or morevalves to regulate the flow of streams through the pipes.

In some implementations, a flow control system can be operated manually.For example, an operator can set a flow rate for each pump and set valveopen or close positions to regulate the flow of the process streamsthrough the pipes in the flow control system. Once the operator has setthe flow rates and the valve open or close positions for all flowcontrol systems distributed across the NGL fractionation plant, the flowcontrol system can flow the streams within a plant or between plantsunder constant flow conditions, for example, constant volumetric rate orsuch flow conditions. To change the flow conditions, the operator canmanually operate the flow control system, for example, by changing thepump flow rate or the valve open or close position.

In some implementations, a flow control system can be operatedautomatically. For example, the flow control system can be connected toa computer system to operate the flow control system. The computersystem can include a computer-readable medium storing instructions (suchas flow control instructions and other instructions) executable by oneor more processors to perform operations (such as flow controloperations). An operator can set the flow rates and the valve open orclose positions for all flow control systems distributed across the NGLfractionation plant using the computer system. In such implementations,the operator can manually change the flow conditions by providing inputsthrough the computer system. Also, in such implementations, the computersystem can automatically (that is, without manual intervention) controlone or more of the flow control systems, for example, using feedbacksystems implemented in one or more plants and connected to the computersystem. For example, a sensor (such as a pressure sensor, temperaturesensor or other sensor) can be connected to a pipe through which aprocess stream flows. The sensor can monitor and provide a flowcondition (such as a pressure, temperature, or other flow condition) ofthe process stream to the computer system. In response to the flowcondition exceeding a threshold (such as a threshold pressure value, athreshold temperature value, or other threshold value), the computersystem can automatically perform operations. For example, if thepressure or temperature in the pipe exceeds the threshold pressure valueor the threshold temperature value, respectively, the computer systemcan provide a signal to the pump to decrease a flow rate, a signal toopen a valve to relieve the pressure, a signal to shut down processstream flow, or other signals.

In some implementations, the techniques described here can beimplemented using a waste heat recovery network that includes 17 heatexchanger units distributed in specific areas of the NGL fractionationplant. As described later, low grade waste heat can be recovered fromseveral processing units at which the heat exchanger units are installedusing two buffer streams, for example, pressurized water, pressurizedliquid propane, oil or such buffer streams. The pressurized water canflow from a dedicated storage tank at a temperature of between 115° F.and 125° F. (for example, a temperature of 120° F.) towards specificunits in the NGL fractionation plant to recover a specific amount ofthermal energy.

The techniques can be implemented to increase the temperature of a firstpressurized water stream from about 120° F. to between 150° F. and 160°F. (for example, about 158° F.) by absorbing thermal energy between 2400MM Btu/h and 2600 MM Btu/h (for example, 2500 MM Btu/h). The pressurizedwater stream at about 158° F. is used to drive a modifiedmulti-effect-distillation (MED) system to produce desalinated water frombrackish water or sea water stream at the rate of about 114,000 m³/day.The temperature of the pressurized water stream is reduced back to about120° F. The pressurized water then flows back to the storage tank andthe processes are repeated.

The techniques can also be implemented to cause the second pressurizedliquid propane stream to absorb between 350 MM Btu/h and 450 MM Btu/h(for example, about 400 MM plant Btu/h) from the NGL fractionationplant. The absorbed thermal energy generates between 90 MM Btu/h and 100MM Btu/h (for example, 98 MM Btu/h) of sub-ambient cooling capacity,which is used in the plant mechanical compression based refrigerationsystem for the system propane refrigerant sub-cooling usingvapor-ejector to decrease the plant refrigeration system powerconsumption by between 10 MW and 20 MW (for example, about 14 MW). Thesecond buffer stream of propane liquid at high pressure is vaporized ina heat exchanger (described and shown later), and used as a motive vaporin the ejector, then condensed in a water cooler to be reused back inthe cycle.

FIG. 1A is a schematic diagram of an example of a low grade waste heatrecovery system. The schematic includes a storage tank 605 to storebuffer fluid, for example, pressurized water, oil, or other bufferfluid. The buffer fluid is flowed to a heat exchanger network 607 which,in some implementations, can include seventeen heat exchangers (forexample, heat exchangers 6 a, 6 b, 6 c, 6 d, 6 e, 6 f, 6 g, 6 h, 6 i, 6j, 6 k, 6 l, 6 m, 6 n, 6 o, 6 p and 6 q), which are described in detaillater. The buffer fluid is flowed through the heat exchanger network 607and heated by streams in the NGL fractionation plant (described later).The heated buffer fluid is flowed to a MED system 609 that can generatepotable water as described later. The temperature of the buffer fluiddecreases as it exits the MED system 609 and flows back to the storagetank 605 to be flowed again through the heat exchanger network 607. Thesystem also includes a cooling sub-system 611 (described later) thatincludes a second buffer stream, for example, pressurized propane thatcan be heated using one or more of the heat exchangers in the heatexchanger network 607 to reduce the cooling requirement of the coolingsub-system. The second buffer fluid sub-cools the compressor feed streamand thus reduces the compressor feed vapor density, which, in turn,reduces the power consumption of the refrigeration compressor. In someimplementations, the techniques described here can be implemented withone of the MED system 609 or the cooling sub-system 611 and without theother of the MED system 609 or the cooling sub-system 611.

FIG. 1B is a schematic diagram of a propane de-hydration section wasteheat recovery system in a NGL fractionation plant. A first heatexchanger 6 a is located in the propane de-hydration section of the NGLfractionation plant. In some implementations, the buffer fluid in thestorage tank 605 is pressurized water at a temperature of between 115°F. and 125° F. (for example, about 120° F.). The pressurized waterstream flows from the storage tank 605 to the first heat exchanger 6 ato cool down the propane de-hydration outlet stream. In turn, thetemperature of the pressurized water stream increases to between 390° F.and 400° F. (for example, about 395° F.). The heated pressurized waterstream flows to the collection header to join other pressurized waterstreams to flow to the MED system 609. The total thermal duty of thefirst heat exchanger 6 a is between 95 MM Btu/h and 100 MM Btu/h (forexample, about 96 MM Btu/h).

FIG. 1C is a schematic diagram of a de-propanizer section waste heatrecovery system in the NGL fractionation plant. A second heat exchanger6 b is located in the de-propanizer section of the NGL fractionationplant. The pressurized water stream flows from the storage tank 605 tothe second heat exchanger 6 b to cool down the de-propanizer overheadoutlet stream. In turn, the temperature of the pressurized water streamincreases to between 130° F. and 140° F. (for example, about 134° F.).The heated pressurized water stream flows to the collection header tojoin other pressurized water streams to flow to the MED system 609. Thetotal thermal duty of the second heat exchanger 6 b is between 950 MMBtu/h and 960 MM Btu/h (for example, about 951 MM Btu/h).

FIG. 1D is a schematic diagram of a butane de-hydrator section wasteheat recovery system in the NGL fractionation plant. A third heatexchanger 6 c is located in the butane de-hydrator section of the NGLfractionation plant. The pressurized water stream flows from the storagetank 605 to the third heat exchanger 6 c to cool down the butanede-hydrator outlet stream. In turn, the temperature of the pressurizedwater stream increases to between 390° F. and 400° F. (for example,about 395° F.). The heated pressurized water stream flows to thecollection header to join other pressurized water streams to flow to theMED system 609. The total thermal duty of the third heat exchanger 6 cis between 40 MM Btu/h and 50 MM Btu/h (for example, about 47 MM Btu/h).

FIG. 1E is a schematic diagram of a de-butanizer section waste heatrecovery system in the NGL fractionation plant. A fourth heat exchanger6 d is located in the de-butanizer section of the NGL fractionationplant. The pressurized water stream flows from the storage tank 605 tothe fourth heat exchanger 6 d to cool down the de-butanizer overheadoutlet stream. In turn, the temperature of the pressurized water streamincreases to between 150° F. and 160° F. (for example, about 152° F.).The heated pressurized water stream flows to the collection header tojoin other pressurized water streams to flow to the MED system 609. Thetotal thermal duty of the fourth heat exchanger 6 d is between 580 MMBtu/h and 590 MM Btu/h (for example, about 587 MM Btu/h).

Also as shown in FIG. 1E, a fifth heat exchanger 6 e is located in thede-butanizer section of the NGL fractionation plant. The pressurizedwater stream flows from the storage tank 605 to the fifth heat exchanger6 e to cool down the de-butanizer bottoms outlet stream. In turn, thetemperature of the pressurized water stream increases to between 255° F.and 265° F. (for example, about 261° F.). The heated pressurized waterstream flows to the collection header to join other pressurized waterstreams to flow to the MED system 609. The total thermal duty of thefifth heat exchanger 6 e is between 50 MM Btu/h and 60 MM Btu/h (forexample, about 56 MM Btu/h).

FIG. 1F is a schematic diagram of a de-pentanizer section waste heatrecovery system in the NGL fractionation plant. A sixth heat exchanger 6f is located in the de-pentanizer section of the NGL fractionationplant. The pressurized water stream flows from the storage tank 605 tothe sixth heat exchanger 6 f to cool down the de-pentanizer overheadoutlet stream. In turn, the temperature of the pressurized water streamincreases to between 160° F. and 170° F. (for example, about 165° F.).The heated pressurized water stream flows to the collection header tojoin other pressurized water streams to flow to the MED system 609. Thetotal thermal duty of the sixth heat exchanger 6 f is between 95 MMBtu/h and 105 MM Btu/h (for example, about 100 MM Btu/h).

FIG. 1G is a schematic diagram of an ADIP regeneration section wasteheat recovery system in the NGL fractionation plant. A seventh heatexchanger 6 g is located in the ADIP regeneration section of the NGLfractionation plant. The pressurized water stream flows from the storagetank 605 to the seventh heat exchanger 6 g to cool down the ADIPregeneration section overhead outlet stream. In turn, the temperature ofthe pressurized water stream increases to between 220° F. and 230° F.(for example, about 227° F.). The heated pressurized water stream flowsto the collection header to join other pressurized water streams to flowto the MED system 609. The total thermal duty of the seventh heatexchanger 6 g is between 10 MM Btu/h and 20 MM Btu/h (for example, about18 MM Btu/h).

Also as shown in FIG. 1G, an eighth heat exchanger 6 h is located in theADIP regeneration section of the NGL fractionation plant. Thepressurized water stream flows from the storage tank 605 to the eighthheat exchanger 6 h to cool down the ADIP regeneration section bottomsoutlet stream. In turn, the temperature of the pressurized water streamincreases to between 165° F. and 175° F. (for example, about 171° F.).The heated pressurized water stream flows to the collection header tojoin other pressurized water streams to flow to the MED system 609. Thetotal thermal duty of the eighth heat exchanger 6 h is between 215 MMBtu/h and 225 MM Btu/h (for example, about 219 MM Btu/h).

FIG. 1H is a schematic diagram of a natural gasoline de-colorizingsection waste heat recovery system in the NGL fractionation plant. Aninth heat exchanger 6 i is located in the natural gasolinede-colorizing section of the NGL fractionation plant. The pressurizedwater stream flows from the storage tank 605 to the ninth heat exchanger6 i to cool down the natural gas de-colorizing section pre-flash drumoverhead outlet stream. In turn, the temperature of the pressurizedwater stream increases to between 205° F. and 215° F. (for example,about 211° F.). The heated pressurized water stream flows to thecollection header to join other pressurized water streams to flow to theMED system 609. The total thermal duty of the ninth heat exchanger 6 iis between 100 MM Btu/h and 110 MM Btu/h (for example, about 107 MMBtu/h).

A tenth heat exchanger 6 j is located in the natural gasolinede-colorizing section of the NGL fractionation plant. The pressurizedwater stream flows from the storage tank 605 to the tenth heat exchanger6 j to cool down the natural gas de-colorizer overhead outlet stream. Inturn, the temperature of the pressurized water stream increases tobetween 225° F. and 235° F. (for example, about 229° F.). The heatedpressurized water stream flows to the collection header to join otherpressurized water streams to flow to the MED system 609. The totalthermal duty of the tenth heat exchanger 6 j is between 50 MM Btu/h and55 MM Btu/h (for example, about 53 MM Btu/h).

FIG. 1I is a schematic diagram of a propane tank vapor recovery sectionwaste heat recovery system in the NGL fractionation plant. An eleventhheat exchanger 6 k is located in the propane tank vapor section of theNGL fractionation plant. The pressurized water stream flows from thestorage tank 605 to the eleventh heat exchanger 6 k to cool down thepropane vapor recovery compressor outlet stream. In turn, thetemperature of the pressurized water stream increases to between 260° F.and 270° F. (for example, about 263° F.). The heated pressurized waterstream flows to the collection header to join other pressurized waterstreams to flow to the MED system 609. The total thermal duty of theeleventh heat exchanger 6 k is between 25 MM Btu/h and 35 MM Btu/h (forexample, about 29 MM Btu/h).

FIG. 1J is a schematic diagram of a propane product refrigerationsection waste heat recovery system in the NGL fractionation plant. Atwelfth heat exchanger 6 l is located in the propane productrefrigeration section of the NGL fractionation plant. The pressurizedwater stream flows from the storage tank 605 to the twelfth heatexchanger 6 l to cool down the propane refrigeration compressor outletstream. In turn, the temperature of the pressurized water streamincreases to between 185° F. and 195° F. (for example, about 192° F.).The heated pressurized water stream flows to the collection header tojoin other pressurized water streams to flow to the MED system 609. Thetotal thermal duty of the twelfth heat exchanger 6 l is between 75 MMBtu/h and 85 MM Btu/h (for example, about 81 MM Btu/h).

FIG. 1K is a schematic diagram of a propane product sub-cooling sectionwaste heat recovery system in the NGL fractionation plant. A thirteenthheat exchanger 6 m is located in the propane product sub-cooling sectionof the NGL fractionation plant. The pressurized water stream flows fromthe storage tank 605 to the thirteenth heat exchanger 6 m to cool downthe propane main compressor outlet stream. In turn, the temperature ofthe pressurized water stream increases to between 235° F. and 245° F.(for example, about 237° F.). The heated pressurized water stream flowsto the collection header to join other pressurized water streams to flowto the MED system 609. The total thermal duty of the thirteenth heatexchanger 6 m is between 60 MM Btu/h and 70 MM Btu/h (for example, about65 MM Btu/h).

FIG. 1L is a schematic diagram of a butane product refrigeration wasteheat recovery system in the NGL fractionation plant. A fourteenth heatexchanger 6 n is located in the butane product refrigeration section ofthe NGL fractionation plant. The pressurized water stream flows from thestorage tank 605 to the fourteenth heat exchanger 6 n to cool down thebutane refrigeration compressor outlet stream. In turn, the temperatureof the pressurized water stream increases to between 140° F. and 150° F.(for example, about 147° F.). The heated pressurized water stream flowsto the collection header to join other pressurized water streams to flowto the MED system 609. The total thermal duty of the fourteenth heatexchanger 6 n is between 45 MM Btu/h and 55 MM Btu/h (for example, about49 MM Btu/h).

FIG. 1M is a schematic diagram of an ethane production section wasteheat recovery system in the NGL fractionation plant. A fifteenth heatexchanger 6 o is located in the ethane production section of the NGLfractionation plant. The pressurized water stream flows from the storagetank 605 to the fifteenth heat exchanger 6 o to cool down the ethanedryer outlet stream during the generation mode. In turn, the temperatureof the pressurized water stream increases to between 405° F. and 415° F.(for example, about 410° F.). The heated pressurized water stream flowsto the collection header to join other pressurized water streams to flowto the MED system 609. The total thermal duty of the fifteenth heatexchanger 6 o is between 20 MM Btu/h and 30 MM Btu/h (for example, about22 MM Btu/h).

FIG. 1N is a schematic diagram of a natural gasoline vapor pressurecontrol section waste heat recovery system in the NGL fractionationplant. A sixteenth heat exchanger 6 p is located in the natural gasolinevapor pressure control section of the NGL fractionation plant. Thepressurized water stream flows from the storage tank 605 to thesixteenth heat exchanger 6 p to cool down the RVP control columnoverhead outlet stream. In turn, the temperature of the pressurizedwater stream increases to between 205° F. and 215° F. (for example,about 211° F.). The heated pressurized water stream flows to thecollection header to join other pressurized water streams to flow to theMED system 609. The total thermal duty of the sixteenth heat exchanger 6p is between 30 MM Btu/h and 40 MM Btu/h (for example, about 36 MMBtu/h).

FIG. 1O is a schematic diagram of an integrated, customized,mono-refrigerant dual vapor compressor-ejector cycle 611. Themono-refrigerant used in the cycle is propane liquid at two identified,operating pressures to serve the mechanical compression refrigerationcycle, and the ejector refrigeration cycle for the compressorsub-cooling to reduce the main refrigeration cycle for the NGLfractionation plant by between 10 MW and 20 MW (for example, about 14.3MW), which represents about 30% of the refrigeration package powerconsumption. Implementations of the cycle shown in FIG. 1O use highpressure liquid propane to directly recover the waste heat in the NGLfractionation plant de-ethanizer overhead stream refrigerationcompressors. To do so, the high pressure liquid propane is flowedthrough a seventeenth heat exchanger 6 q having a thermal duty between400 MM Btu/h and 410 MM Btu/h (for example, about 403 MM Btu/h). Thehigh pressure liquid propane at a pressure of between 15 bar and 25 bar(for example, 20 bar) and a temperature of between 80° F. and 90° F.(for example, 88° F.) is fully vaporized in the seventeenth heatexchanger 6 q. The vapor propane is directed to work as a motive streamin a vapor ejector.

In the compressor-ejector cycle, the first liquid propane stream flowsfrom a high pressure feed drum at a pressure of between 20 bar and 30bar (for example, 24 bar) located after the refrigeration compressorafter-cooler to an eighteenth heat exchanger 6 r that has a thermal loadof between 90 MM Btu/h and 100 MM Btu/h (for example, 98 MM Btu/h). Thissub-cooler uses another stream of liquid propane from the ejector cycleas shown in FIG. 1O. The second liquid propane stream is at a pressureof between five bar and 15 bar (for example, 10.8 bar). A small portionof this second propane liquid stream (for example about 20%) isthrottled in a throttling valve to a pressure between five bar and 10bar (for example, 6.25 bar) to generate chilling capacity at atemperature between 45° F. and 55° F. (for example, about 49° F.) for athermal load of between 90 MM Btu/h and 100 MM Btu/h (for example, 98 MMBtu/h). The chilling capacity is sufficient to satisfy the needs of theNGL fractionation plant de-ethanizer overhead stream propanerefrigeration compressor stream sub-cooling. The remainder of the secondpropane stream is pumped to a higher pressure of between 15 bar and 25bar (for example, about 20 bar).

The two propane vapor streams—the first out of the sub-cooler at atemperature of between 50° F. and 60° F. (for example, 55° F.) and apressure between 3 bar and 10 bar (for example, 5.9 bar), and the secondout of the seventeenth heat exchanger at a temperature between 125° F.and 135° F. (for example, 131° F. and a pressure between 15 bar and 25bar (for example, 19.3 bar)—are mixed in a customized ejector to get avapor stream at the desired pressure for condensation using coolingwater at a temperature between 70° F. and 80° F. (for example, 77° F.).The propane stream out of the ejector at a pressure between five bar and15 bar (for example, 11 far) and a temperature between 95° F. and 105°F. (for example, 99° F.) is condensed and flowed to the ejector cyclefor the compressor stream sub-cooling using the compressors low gradewaste heat directly.

FIG. 1P is a schematic diagram representing an example of a modified MEDsystem 609 configured to produce potable water using the pressurizedwater heated by the heat exchanger network 607. The modified MED systemrepresented by FIG. 1P can be implemented to produce about 114,000m³/day of potable water. The system includes multiple trains, forexample, three trains, in series. The trains can be independent fromeach other. Each train, in turn, can include multiple effects having thesame design. An effect includes a heat exchanger that uses the waterheated by the heat exchanger network 607 to distill the brackish waterinto fresh, potable water and brine. The effects can be coupled inparallel. In some implementations, the hot waste stream heated by theheat exchanger network 607 starts at between 65° C. and 75° see (forexample, about 70° C.) when flowed into the MED system and ends atbetween 45° C. 55° C. (for example, 49° C.) when flowed out of the MEDsystem. The temperature of brine from which the potable water isgenerated is between 55° C. and 65° C. (for example, about 58° C.).

In the schematic diagram shown in FIG. 1P, the MED system 609 includesthree trains. The first train 620 a can include six effects connected inseries. The second train 620 b can include four effects connected inseries. The third train 620C can include two effects connected inseries. The number of trains and the number of effects in thisimplementation are examples. The MED system 609 can have fewer or moretrains, with each phase having fewer or more effects. The arrangementshown in FIG. 1P represents a best match between the heat duty load andreasonable temperature drop between effects that renders best waterproduction from the available waste heat.

The MED system feed water is distributed onto the heat exchanger of thefirst effect in all of the trains of the system 609. The high pressurewater stream, heated by the heat exchanger network 607, flows throughthe heat exchanger and releases its energy to the distributed feed waterto evaporate a portion of the feed water. The produced vapor thencondenses in the heat exchanger of the second effect to evaporate morewater in that effect. The brine from the first effect is then purged. Atthe second effect, the evaporated feed water goes on to power the thirdeffect with the resulting brine being drained from the bottom of theeffect. This process continues to the last effect within each train withthe corresponding produced vapor entering the condenser section to becondensed by the incoming saline water acting as a coolant. Part of thepre-heated saline water is then sent to the various effects as feedwater. The saline water temperature can be between 25° C. and 35° C.(for example, about 28° C.), and the feed water temperature can bebetween 30° C. and 40° C. (for example, about 35° C.). The temperaturedrop from one effect to the next can be between 1° C. and 5° C. (forexample, 3° C.).

In some implementations, a steam booster unit is included in the MEDsystem to better exploit the waste heat stream to increase the freshwater yield. The steam booster unit includes an evaporator powered bythe outgoing waste heat source of the MED system. The vapor generatedfrom the steam booster unit is introduced into a suitable effect of theMED system. The inclusion of the steam booster unit in the MED systemcan increase the production rate to the extent allowed by thetemperature drop across the steam booster unit.

In some implementations, one or more flashing chambers can be includedin the MED system to improve the efficiency of the MED system, toextract more energy from the waste heat, and to utilize the extractedenergy to generate stream, thereby increasing fresh water production. Insuch implementations, the outlet source from the MED system goes on toheat the feed water via a liquid-liquid heat exchanger, which isslightly heated by the outlet brine stream from the last flashingchamber. The heated feed water goes through a series of flashingchambers. The vapor generated from each stage of the flashing is theninjected into an effect of the MED system for further boosting.

By identifying a best match between the waste heat load temperatureprofile and the number of effects used in each train, the quantity ofwater that can be generated using the MED system is optimized.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the followingclaims.

1. A system comprising: a waste heat recovery heat exchanger networkthermally coupled to a plurality of heat sources of a Natural Gas Liquid(NGL) fractionation plant, the heat exchanger network configured torecover at least a portion of heat generated at the plurality of heatsources; and a first sub-system thermally coupled to the waste heatrecovery heat exchanger to receive at least a first portion of heatrecovered by the heat exchanger network, the first sub-system configuredto perform one or more operations using at least the first portion ofheat recovered by the heat exchanger network.
 2. The system of claim 1,further comprising a second sub-system thermally coupled to the wasteheat recovery heat exchanger to receive at least a second portion ofheat recovered by the heat exchanger network, the second sub-systemseparate and distinct from the first sub-system, the second sub-systemconfigured to perform one or more operations using at least the secondportion of heat recovered by the heat exchanger network.
 3. The systemof claim 1, further comprising a control system connected to the heatexchanger network and the first sub-system or the heat exchanger networkand the second sub-system or the heat exchanger network, the firstsub-system and the second sub-system, the control system configured toflow fluids between the NGL fractionation plant, the heat exchangernetwork one or both of the first sub-system or the second sub-system. 4.The system of claim 1, wherein the fluids comprise one or more of a NGLfractionation plant stream or a buffer fluid.
 5. The system of claim 1,wherein the plurality of heat sources comprise: a first plurality ofsub-units of the NGL fractionation plant, the first plurality ofsub-units comprising a propane dehydration section, a de-propanizersection, a butane de-hydrator section, and a de-butanizer section; asecond plurality of sub-units of the NGL fractionation plant, the secondplurality of sub-units comprising a de-pentanizer section, anAmine-Di-Iso-Propanol (ADIP) regeneration section, a natural gasde-colorizing section, a propane vapor recovery section and a propaneproduct refrigeration section; and a third plurality of sub-units of theNGL fractionation a propane product sub-cooling section, a butaneproduct refrigeration section, an ethane production section and a ReidVapor Pressure (RVP) control section.
 6. The system of claim 1, whereinthe heat exchanger network comprises a plurality of heat exchangers. 7.The system of claim 1, wherein the plurality of heat exchangerscomprises: a first subset comprising one or more of the plurality ofheat exchangers thermally coupled to the first plurality of sub-units ofthe NGL fractionation plant.
 8. The system of claim 1, wherein the firstsubset comprises: a first heat exchanger thermally coupled to thepropane dehydration section, the first heat exchanger configured to heata first buffer stream using heat carried by a propane de-hydrationoutlet stream from the propane de-hydration section; a second heatexchanger thermally coupled to the de-propanizer section, the secondheat exchanger configured to heat a second buffer stream using heatcarried by a de-propanizer overhead outlet stream from the de-propanizersection; a third heat exchanger thermally coupled to the butanede-hydrator section, the third heat exchanger configured to heat a thirdbuffer stream using heat carried by a butane de-hydrator outlet stream;a fourth heat exchanger thermally coupled to the de-butanizer section,the fourth heat exchanger configured to heat a fourth buffer streamusing heat carried by a de-butanizer overhead outlet stream from thede-butanizer section; and a fifth heat exchanger thermally coupled tothe de-butanizer section, the fifth heat exchanger configured to heat afifth buffer stream using heat carried by a de-butanizer bottoms outletstream from the de-butanizer section.
 9. The system of claim 1, whereinthe plurality of heat exchangers comprises: a second subset comprisingone or more of the plurality of heat exchangers thermally coupled to thesecond plurality of sub-units of the NGL fractionation plant.
 10. Thesystem of claim 1, wherein the second subset comprises: a sixth heatexchanger thermally coupled to the de-pentanizer section, the sixth heatexchanger configured to heat a sixth buffer stream using heat carried bya de-pentanizer overhead outlet stream from the de-pentanizer section; aseventh heat exchanger thermally coupled to the ADIP regenerationsection, the seventh heat exchanger configured to heat a seventh bufferstream using heat carried by an ADIP regeneration section overheadoutlet stream; an eighth heat exchanger thermally coupled to the ADIPregeneration section, the eighth heat exchanger configured to heat aneighth buffer stream using heat carried by an ADIP regeneration sectionbottoms outlet stream; a ninth heat exchanger thermally coupled to thenatural gas de-colorizing section, the ninth heat exchanger configuredto heat a ninth buffer stream using heat carried by a natural gasde-colorizing section pre-flash drum overhead outlet stream; a tenthheat exchanger thermally coupled to the natural gas de-colorizingsection, the tenth heat exchanger configured to heat a tenth bufferstream using heat carried by a natural gas de-colorizer overhead outletstream; an eleventh heat exchanger thermally coupled to the propanevapor recovery section, the eleventh heat exchanger configured to heatan eleventh buffer stream using heat carried by a propane vapor recoverycompressor outlet stream; and a twelfth heat exchanger thermally coupledto the propane product refrigeration section, the twelfth heat exchangerconfigured to heat a twelfth buffer stream using heat carried by apropane refrigeration compressor outlet stream from the propane productrefrigeration section.
 11. The system of claim 1, wherein the pluralityof heat exchangers comprises: a third subset comprising one or more ofthe plurality of heat exchangers thermally coupled to the thirdplurality of sub-units of the NGL fractionation plant.
 12. The system ofclaim 1, wherein the third subset comprises: a thirteenth heat exchangerthermally coupled to the propane product sub-cooling, the thirteenthheat exchanger configured to heat a thirteenth buffer stream using heatcarried by a propane main compressor outlet stream from the propaneproduct sub-cooling section; a fourteenth heat exchanger thermallycoupled to the butane product refrigeration section, the fourteenth heatexchanger configured to heat a fourteenth buffer stream using heatcarried by a butane refrigeration compressor outlet stream from thebutane product refrigeration section; a fifteenth heat exchangerthermally coupled to the ethane production section, the fifteenth heatexchanger configured to heat a fifteenth buffer stream using heatcarried by an ethane dryer outlet stream; and a sixteenth heat exchangerthermally coupled to the RVP control section, the sixteenth heatexchanger configured to heat a sixteenth buffer stream using heatcarried by a RVP control column overhead outlet stream.
 13. The systemof claim 1, further comprising a storage tank configured to store thebuffer streams, wherein the control system is configured to flow thebuffer streams from the storage tank to the heat exchanger network. 14.The system of claim 1, wherein the buffer stream comprises pressurizedwater.
 15. The system of claim 1, wherein the first sub-system comprisesa modified multi-effect-distillation (MED) system configured to producepotable water using at least the portion of heat recovered by the heatexchanger network.
 16. The system of claim 1, wherein the MED systemcomprises a plurality of trains, wherein each train is configured toreceive the heated buffer fluid from the heat exchanger network and toproduce potable water using the heat carried by the heated buffer fluid.17. The system of claim 1, wherein the MED system comprises threetrains, wherein a first train comprises six effects, a second traincomprises four effects and a third train comprises two effects.
 18. Thesystem of claim 1, wherein the second sub-system comprises a coolingsub-system configured to generate cooling capacity to cool at least aportion of the NGL fractionation plant.
 19. The system of claim 1,wherein cooling sub-system comprises a mono-refrigerant dual vaporcompressor-ejector cycle.
 20. The system of claim 1, wherein thecompressor-ejector cycle comprises a first propane stream that isvaporized to generate the cooling capacity.
 21. The system of claim 1,wherein the third subset of heat exchangers comprises a seventeenth heatexchanger thermally coupled to the de-ethanizer section, the seventeenthheat exchanger configured to heat the first propane stream using heatcarried by a de-ethanizer refrigeration compressor outlet stream fromthe de-ethanizer section.
 22. The system of claim 16, wherein the MEDsystem comprises a first phase comprising three trains, wherein a firsteffect in a first train of the three trains in the first phase isconnected with a first effect of a second train of the three trains inthe first phase and with a first effect of a third train of the threetrains in the first phase.
 23. The system of claim 22, wherein the MEDsystem comprises a second phase comprising three trains, wherein a firsteffect in a first train of the three trains in the second phase isconnected with a first effect of a second train of the three trains inthe second phase and with a first effect of a third train of the threetrains in the second phase.
 24. The system of claim 23, wherein the MEDsystem comprises a third phase comprising three trains, wherein a firsteffect in a first train of the three trains in the third phase isconnected with a first effect of a second train of the three trains inthe third phase and with a first effect of a third train of the threetrains in the third phase.